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See detailThe catalytic mechanism of beta-lactamases: NMR titration of an active-site lysine residue of the TEM-1 enzyme.
Damblon, Christian ULg; Raquet, X.; Lian, L. Y. et al

in Proceedings of the National Academy of Sciences of the United States of America (1996), 93(5), 1747-52

Beta-Lactamases are widespread in the bacterial world, where they are responsible for resistance to penicillins, cephalosporins, and related compounds, currently the most widely used antibacterial agents ... [more ▼]

Beta-Lactamases are widespread in the bacterial world, where they are responsible for resistance to penicillins, cephalosporins, and related compounds, currently the most widely used antibacterial agents. Detailed structural and mechanistic understanding of these enzymes can be expected to guide the design of new antibacterial compounds resistant to their action. A number of high-resolution structures are available for class A beta-lactamases, whose catalytic mechanism involves the acylation of a serine residue at the active site. The identity of the general base which participates in the activation of this serine residue during catalysis has been the subject of controversy, both a lysine residue and a glutamic acid residue having been proposed as candidates for this role. We have used the pH dependence of chemical modification of epsilon-amino groups by 2,4,6,-trinitrobenzenesulfonate and the pH dependence of the epsilon-methylene 1H and 13C chemical shifts (in enzyme selectively labeled with [epsilon-13C]lysine) to estimate the pKa of the relevant lysine residue, lysine-73, of TEM-1 beta-lactamase. Both methods show that the pKa of this residue is > 10, making it very unlikely that this residue could act as a proton acceptor in catalysis. An alternative mechanism in which this role is performed by glutamate-166 through an intervening water molecule is described. [less ▲]

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See detailThe structures and catalytic mechanisms of active-site serine beta-lactamases.
Lamotte, Josette ULg; Knox, J.; Kelly, J. A. et al

in Biotechnology & Genetic Engineering Reviews (1994), 12

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See detailConformational analysis of β and γ-lactam antibiotics
Lamotte, Josette ULg; Dive, Georges ULg; Ghuysen, Jean-Marie ULg

in European Journal of Medicinal Chemistry (1991), 26(1), 43-50

Geometry optimization, superimposition searches and conformational analysis carried on several lactam antibiotics show that reactivity with the active-site serine penicillin-binding proteins is related to ... [more ▼]

Geometry optimization, superimposition searches and conformational analysis carried on several lactam antibiotics show that reactivity with the active-site serine penicillin-binding proteins is related to a particular spatial disposition of 2 flanking functional groups - namely a C = O or C-OH on 1 side and a carboxylate on the other - with respect to the central scissile amide bond. Such a binding entity is found in one of the most stable conformers of the tripeptide diacetyl-L-Lys-D-Ala-D-Ala conferring substrate activity, and in benzylpenicillin, cephapyrin, thienamycin, gamma-lactam, the 6-spiro-epoxypenicillin S and in one epimer of lactivicin, conferring inactivating potency. This binding entity generates a particular electronic distribution and the fact that it is conserved in compounds belonging to very different chemical families strongly suggests that it is an important feature required for enzyme recognition. [less ▲]

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See detailActive-site-directed inactivators of the Zn2+-containing D-alanyl-D-alanine-cleaving carboxypeptidase of Streptomyces albus G.
Charlier, Paulette ULg; Dideberg, Otto; Jamoulle, Jean-Claude et al

in Biochemical Journal (1984), 219(3), 763-772

Several types of active-site-directed inactivators (inhibitors) of the Zn2+-containing D-alanyl-D-alanine-cleaving carboxypeptidase were tested. (i) Among the heavy-atom-containing compounds examined ... [more ▼]

Several types of active-site-directed inactivators (inhibitors) of the Zn2+-containing D-alanyl-D-alanine-cleaving carboxypeptidase were tested. (i) Among the heavy-atom-containing compounds examined, K2Pt(C2O4)2 inactivates the enzyme with a second-order rate constant of about 6 X 10(-2)M-1 X S-1 and has only one binding site located close to the Zn2+ cofactor within the enzyme active site. (ii) Several compounds possessing both a C-terminal carboxylate function and, at the other end of the molecule, a thiol, hydroxamate or carboxylate function were also examined. 3-Mercaptopropionate (racemic) and 3-mercaptoisobutyrate (L-isomer) inhibit the enzyme competitively with a Ki value of 5 X 10 X 10(-9)M. (iii) Classical beta-lactam compounds have a very weak inhibitory potency. Depending on the structure of the compounds, enzyme inhibition may be competitive (and binding occurs to the active site) or non-competitive (and binding causes disruption of the protein crystal lattice). (iv) 6-beta-Iodopenicillanate inactivates the enzyme in a complex way. At high beta-lactam concentrations, the pseudo-first-order rate constant of enzyme inactivation has a limit value of 7 X 10(-4)S-1 X 6-beta-Iodopenicillanate binds to the active site just in front of the Zn2+ cofactor and superimposes histidine-190, suggesting that permanent enzyme inactivation is by reaction with this latter residue. [less ▲]

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See detailConformational analysis of peptide substrates and inhibitors of the Zn2+ G and serine R61 D-alanyl-D-alanine peptidases
De Coen, Jean-Louis; Lamotte, Josette ULg; Ghuysen, Jean-Marie ULg et al

in European Journal of Biochemistry (1981), 121(1), 221-232

The tripeptide Nα,Nɛ-diacetyl-l-lysyl-d-alanyl-d-alanine (Ac2- l-LLys1-dAIa2-dAIa3), which is the standard substrate of the Zn2+ G and serine R61 d-alanyl-d-alanine peptidases, and several ldd tripeptide ... [more ▼]

The tripeptide Nα,Nɛ-diacetyl-l-lysyl-d-alanyl-d-alanine (Ac2- l-LLys1-dAIa2-dAIa3), which is the standard substrate of the Zn2+ G and serine R61 d-alanyl-d-alanine peptidases, and several ldd tripeptide analogues where the size and/or the electrical charge of the side chains at position 1, 2 or 3 have been modified (alterations affecting more than one position at the same time were not investigated) have been submitted to conformational analyses based on both short-range and long-range interactions. Among the many backbone conformers of minimal energy of the øii space that have been characterized, four types of conformers are the most probable ones. Depending on the peptides, these conformers may have varying relative probability P values so that the leader conformer is not always the same, but, in all cases, the sum of their P values is 90% or more. With the Gly1, Gly2 or Gly3 analogues (which encompass a larger conformational space), the above ∑P values are still as high as 35–50%. All the above tripeptides bind to the serine d-alanyl-d-alanine peptidase and with the exception of the Gly3 and Gly2 analogues, to the Zn2+d-alanyl-d-alanine peptidase with virtually the same efficacy, at least within a range of variation of the Km values for the substrates or the Ki values for the inhibitors, which is less than one order of magnitude. Structural variations at position 1, 2 or 3 in the peptides that are compatible with efficient binding are not necessarily compatible with substrate activity, thus converting the modified peptides into competitive inhibitors. In particular, substrate activity requires a long side chain at position 1 in the peptides. Conformational analyses of Ac2-lLys-dAla-dAla show that the main backbone has a tendency to adopt a ring-like shape from which the lLYS side chain protrudes as an extended structure. This latter structure forms with the C-terminal d-alanyl-d-alanine an angle varying between 120° and 180° (depending on the conformers) so that its N-terminal acetyl group is about 1–1.5 nm apart from the scissile amide bond. High turnover numbers (at enzyme saturation) also require a dAla at position 2 with both d-alanyl-d-alanine peptidases and at position 3 in the case of the serine d-alanyl-d-alanine peptidase. Finally, all the conformers of the lAla2 and lAla3 analogues of Ac2-lLys-dAla-dAla fall outside the backbone conformational space that comprises the φiφi angles exhibited by the four types of conformers of the ldd tripeptides. The lAla2 and lAla3 tripeptide analogues do not bind to the serine d-alanyl-d-alanine peptidase (at least at a 10 mM concentration) but they behave as noncompetitive inhibitors of the Zn2+d-alanyl-d-alanine peptidase. [less ▲]

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See detailStructure d'un nouvel alcaloïde bisindolinique: complexe moléculaire 1:1 Sungucine-Acétone
Dupont, Léon; Dideberg, Otto; Lamotte, Josette ULg et al

in Acta Crystallographica. Section B-Structural Crystallography and Crystal Chemistry (1980), B 36

Sungucine ( found only in Strychnos icaja ) represents a new type of bisindolinic alkaloid with an unusual C(23)-C(5') bond between the two parts of the molecule, which have the same stereochemistry. Ring ... [more ▼]

Sungucine ( found only in Strychnos icaja ) represents a new type of bisindolinic alkaloid with an unusual C(23)-C(5') bond between the two parts of the molecule, which have the same stereochemistry. Ring D (and D') is almost in a boat conformation and C(2)-C(16) is cis. There are only van der Waals interactions in the orthorombic crystals of the molecular complex 1:1 sungucine-acetone. [less ▲]

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See detailIsolation and structure of sungucine, a new type of bisindoline alkaloid
Lamotte, Josette ULg; Dupont, Léon; Dideberg, Otto et al

in Tetrahedron Letters (1979), (43), 4227-4228

From the roots of Strychnos icaja BAILLON, an unsymmetrical dimeric alkaloid has been isolated and called sungucine. Its original structure has been established by X-Ray diffraction; UV,IR,MS and NMR data ... [more ▼]

From the roots of Strychnos icaja BAILLON, an unsymmetrical dimeric alkaloid has been isolated and called sungucine. Its original structure has been established by X-Ray diffraction; UV,IR,MS and NMR data are also given. [less ▲]

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See detailStructure Cristalline et Moléculaire de la Picrotoxine, C15H16O6.C15H18O7
Dupont, Léon; Dideberg, Otto; Lamotte, Josette ULg et al

in Acta Crystallographica. Section B-Structural Crystallography and Crystal Chemistry (1976), B32(11), 2987-2993

Picrotoxin is the toxic constituent of Anamirta cocculus fruits. Crystals of picrotoxin are monoclinic and are an addition component of two almost identical molecules :picrotoxinin, C15H16O6, and picrotin ... [more ▼]

Picrotoxin is the toxic constituent of Anamirta cocculus fruits. Crystals of picrotoxin are monoclinic and are an addition component of two almost identical molecules :picrotoxinin, C15H16O6, and picrotin, C15H18O7.The structure of each molecule is compared with the crystal structure of alpha1-bromopicrotoxinin. [less ▲]

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